The field of the invention is medical imaging systems and more specifically includes systems for compensating for misalignment of two or more image data sets due to support table deflection.
The medical imaging industry has developed many different types of imaging systems that are useful for diagnostic purposes. Each different system typically has particular uses for which it is advantageous. For example, computerized tomography (CT) systems that employ X-rays are useful for generating static images of bone and the like while positron emission tomography (PET) systems are useful for generating dynamic or functional images of dynamic occurrences such as blood flow and the like.
For various reasons it is advantageous to generate images that include both static and functional characteristics. To this end one solution has been to sequentially use separate imaging systems to gather both functional and static imaging data sets and then combine those sets or corresponding images to generate unified functional/static images. For example, first a CT system may be used to generate a CT image and second a PET system may be used to generate a PET image, the two images being combined thereafter to generate the unified image.
Unfortunately, systems having two separate imaging configurations have several shortcomings. First, there has to be some way to align the functional and dynamic images so that the unified image reflects relative anatomical positions precisely. To this end fiducial markers have been employed. For example, a metallic button with a positron emitter can be placed on the surface of a patient's skin which is detectable by both the CT and PET systems. By aligning the marker in the resulting images the images can be aligned.
Second, where two separate imaging configurations are employed a patient has to be moved from one configuration to the next between acquisition sessions. Movement increases the likelihood that the patient's positions during the two imaging sessions will change thus tending to reduce the possibility of accurate alignment (i.e., relative positions of organs or the like could change during movement). The possibility of misalignment is exacerbated by the fact that often imaging session schedules will not allow both CT and PET imaging processes to be performed during the same day. Thus, overall diagnostic value of the resulting unified image can be reduced appreciably through movement between acquisition periods.
One solution to eliminate the need to move patient's between acquisition periods is to provide a dual CT-PET imaging system like the one illustrated in FIG. 1. In these types of systems both a CT imaging configuration 14 and a PET imaging configuration 16 are arranged sequentially along a single translation axis 19 with their relative positions fixed. A support 12 for a support table 18 is positioned adjacent the system with the table 18 moveable along the translation axis 19. Here the CT and PET systems can be used simultaneously or sequentially to acquire both CT and PET sets of imaging data in a relatively short time and without moving the patient from one configuration to another. The end result is less patient movement, less time to gather required data and better alignment of resulting images to provide a more accurate unified image.
One problem with dual imaging systems is that each of the CT and PET configurations typically include a gantry to support a detector or series of detectors laterally displaced from the translation axis 19. For this reason the translation axis 19 is relatively long and the support table 18 needs to extend a relatively long distance in order to accommodate the system configurations.
While every effort is made to provide stiff supports and tables so that vertical alignment within CT and PET imaging areas can be maintained, when a patient is positioned on a table and the table is extended to accommodate the axial length of dual imaging systems it has been found that the tables often sag such that the CT and PET data sets collected are not aligned along the translation axis 18. Exacerbating matters is the fact that over time stiffness of some supports and tables has been known to deteriorate. While stiffer tables and supports is an option, increased stiffness is a relatively expensive proposition as exotic configurations and materials have to be used to achieve greater stiffness.